The Cell Biology Department at Duke University has a strong program for the study of biological structure and function, with x-ray diffraction as a major investigative tool. Five NIH supported projects currently use x-ray diffraction facilities in this department. These include: (1) measurements of short- and long-range pressures between lipid bilayer and biological membrane surfaces, (2) determination of concentration of total solids in bleached and dark-adapted photoreceptors, (3) evaluation of 2-D calcium ATPase crystals for analysis by electron microscopy, (4) studies of conformational rearrangements of myosin cross-bridges associated with force production in insect flight muscle, and (5) analysis of the mechanisms of bilayer fusion induced by polyethylene glycol. These projects have put an increasing demand on the x-ray generators currently available in this department, all of which are over 20 years old and rapidly becoming unreliable. In addition, our most heavily used generator is a stationary anode model, which does not have the power for some of our studies, particularly those involving biological membranes and muscle. We are requesting funds for the purchase of a Rigaku RU200 rotating anode x-ray generator for use as a shared facility among four researchers at Duke University and one at the nearby University of North Carolina. This generator should overcome the deficiencies of our current generators and meet our needs for a reliable and relatively bright source of x-rays.